DesertRat wrote on 04/16/16 at 17:48:17:a pcv valve that is totally plugged up with sludge can cause this ... check the vent tube at the top left of the head goes into the air filter box ...
or
it needs a rebuild ...
Dad screwed up big time back in the 70's over his Mustang that had PCV valve trouble. Was "blowing oil out the dipstick." He changed the engine, injured his back, and got discouraged and sold it because it didn't perform like the old engine. Went from a 260 to a 289. It was a 1964.5 year model.
By the way, he hurt his back actually carrying that 289 V8 in his arms.
Sometimes it helps to know what's going on.